The present invention is directed to a method of reducing distorsions in a light waveguide of a magneto-optical device for providing a magneto-optical device having a light waveguide with a low birefringence.
For magneto-optical devices, it is necessary to have light waveguides in which the polarization relationship of the guided light are falsified or distorted as little as possible and particularly a waveguide which avoids birefringence. A magneto-optical device of this sort is, for example, an optical measuring transformer or transducer which is a device for measurement of strong magnetic fields. This is accomplished by a polarized light being conveyed by a light waveguide and guided through a magnetic field. For the measurement of the field, the influence of the magnetic field on the polarization level of the light is determined. Another example of a magneto-optical device is a magneto-optical gyroscope. Fiber optical waveguides with birefringence will disturb the information contained in the plane polarized beam and, therefore, cause false measurements, in particular, if the birefringence is temperature dependent.
Previously, for the direction of the light through such a magneto-optical device, light waveguides of a cylindrical glass jacket or tube are used and contained a liquid which guided the light. Because of the isotropy of the liquid, no privileged directions were formed in this type of light guide and thus the polarization relationship of the light was not disturbed. Nevertheless, these liquid light guides have other disadvantages. For example, they require a more expensive and involved system of construction and are strongly temperature dependent with regard to their mechanical and their magneto-optical characteristics.
Usual fiber optical waveguides, which consist of a glass core and a glass cladding or jacket, which glass cladding has a lower index of refraction than the glass core, are not suitable for magneto-optical uses. In particular, these glass fiber optical waveguides have a significant birefringence. The reason for this birefringence is still not well explained. In the usual fiber optical waveguide, the fiber core generally consists of quartz glass which has been doped with a GeO.sub.2 or P.sub.2 O.sub.5. Fluctuations in the concentration of the doping material can, for example, lead to tensions or stresses which negatively influence the polarization characteristic of the fiber. So, for example, in the case of the usual commercial GeO.sub.2 doped quartz glass fibers, a high depolarization of the light beam has been observed. Also, for example, the birefringence is all the more stronger when the cross section of the glass core deviates from a circular form. Further, large differences in the thermal coefficient of expansion of the core material and the cladding material leads to stresses and to depolarization.